1. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. DORIS campaigns at Dome Concordia, Antarctica in 1993 and 1999-2000 C. Vincent 1, JJ. Valette 2, L. Soudarin 2, JF. Crétaux 3, B. Legresy 3, F. Rémy 3, A. Capra 4 1 LGGE/CNRS, Laboratoire de Glaciologie et de Géophysique de l’Environnement, Grenoble, France 2 CLS, Collecte Localisation Satellites, Ramonville, France 3 LEGOS/GRGS (CNES/CNRS-UPS), Toulouse, France 4 Istituto de Topografia, Geodesia e Geofisica Mineraria, Universita de Bologna DORIS DAYS 2-3 May 2000

2. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Dome Concordia Concordia : French - Italian glaciological research project (LGGE/DISTART,...) topics : snow accumulation, ice thickness, ice flowing … EPICA : European project for deep ice coring topics : ice cap response to global climate changes, north-south hemisphere coupling... Base on the Antarctic continent open from December to February since 1996, permanent by 2003 Management by IFRTP

3. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Why a drilling location there? Interests of this continental dome : T < -25°C, no summer ice melting excellent location for a whole Antarctic record 3300 m thickness  long and continuous climate record 400 Ka least disturbed ice sequence at the dome summit (minimal ice flow correction)

4. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Main geodetic informations needed QuestionsTechnique 1996 Position of the dome summit ? ERS-1 altimeter (Rémy) GPS (Ceffalo) Airbone VHF radar (Tabacco) for layering 2000 Absolute 3D ice surface velocity ?DORIS 1993 and 1999-2000 (C. Vincent) local deformation ?GPS 1995-1998 (A. Capra) ERS-1 Insar 1996 (B. Legrésy)

5. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Charming but constraining place (1) Equipment suffering : beacon specification from -20° to +55°C gradient < 10°/hr Generator failures  USO drift of a few 10-11/jr (still under specification)

6. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Charming but constraining place (2) Scientist suffering : Dry but freezing summertime (4 g/cm 2 equivalent water a year) What geodetic « monumentation » ? How to prevent from stake subsidence? How to measure snow accumulation ?

7. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. CLS DORIS Data Processing Center, Toulouse Onboard instrument control Telemetry acquisition and preprocessing Operational orbit and stations position (48 h delay) Spot 4 data validation 2 days delay Dome C operational location (height)

8. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. DORIS campaigns DORIS observations at main point (D1)  Drilling site D1 Doris main site (IERS id. : 66009 in 93 - 66013 in 99) D2 Doris ancillary site (66014) 10 km 5 m isolines

9. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Data processing At GRGS/CLS DORIS data analysis center for IERS and IDS with GINS/DYNAMO software and the most recent models : GRIM5 (Biancale et al.), atmospheric effects Geodetic parameters : satellites orbit, stations position and velocity Empirical coefficients : air drag, solar pressure radiation, Hill residual forces, zenital tropospheric delay Instrumental parameters: USO frequency bias

10. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Absolute velocity corrections Antarctic plate tectonic motion deduced from DORIS at Dome Concordia : in latitude : -9.4 mm/yr in longitude : 0.4 mm/yr (Crétaux et al. 1998) Post glacial rebound uplift : less than 1-3 mm/yr

11. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Preliminary DORIS results 2 months global network solutions (Nov-Dec 93 and 99) Typical precision : 7 parameters Helmert transformation (versus solution 1993) 3D coordinates changes over 6 years (same réf. point, plate motion is removed)

12. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Contribution to ice core analysis (1) DORIS 3D absolute velocity gives an input for numerical ice flow model in depth. Essential for cores dating. DORIS results in horizontal : 0.6 cm/yr in latitude -1.8 cm/yr in longitude agree with balance model between snow accumulation and ice flow induced by gravity (figure) (Legresy)

13. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Contribution to ice core analysis (2)  DORIS results in vertical : -9.6 cm/yr Probably the first absolute determination of the vertical velocity  observed snow accumulation at the top of the stake (height level change) : 35 cm over the 6 years while 10 cm/yr is expected (Petit et al.) Error observation or snowfall anomaly ?  Mass balance between snowfall and ice flow towards the ocean ? Sea level and climat changes implications

14. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Contribution to radar remote sensing observations SAR Interferometry maps relative surface velocity in the line of sight ERS SAR interferogram (69 days interval) shows maximum of 3 cm/yr DORIS gives the absolute ITRF tie of the velocity fields Space Radar Altimetry maps ice topography within 10-20 cm but an in-situ calibration is needed, moreover the signal penetration depends on the snow structure DORIS gives the height reference and its variations in time

15. C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France. Conclusions  DORIS (93-99) component of CONCORDIA project confirms that a very low absolute horizontal ice surface velocity affects the EPICA drilling (< 2 cm/yr). Also vertical flow determination as a first.  DORIS absolute geodetic approach fully completes GPS survey and calibrates radar satellite remote sensing techniques (with future missions ERS2, ENVISAT, IceSat, CRYOSAT).  Proposal to IDS for repeated DORIS campaigns at Dome Concordia